The present invention relates to a system for 3-dimensional viewing of objects such as printed circuit boards, hybrid microelectronics assemblies, eye implant lenses, medical devices, and the like, where close inspection is necessary to pinpoint any irregularities or defects which may be on a relatively small scale.
In order for small defects or irregularities on such objects to be seen and understood, the object must normally be magnified. It is also desirable to see a 3-dimensional view of the object so that the depth of any edges in the object can be understood, and also so that the observer can see around edges and observe defects or features of the object which would otherwise be hidden or unclear in a 2-dimensional view.
Existing devices for viewing such objects include magnifying lenses and screen projectors. Magnifying lenses are limited in magnifying power and field of view, and are tiring to use. Screen projectors produce a flat 2-dimensional image of limited resolution.
The 3-dimensional effect in normal vision is produced by two slightly different retinal images being produced by each eye, with the brain combining these images to produce an impression of depth. This is known as the "stereoscopic" effect.
This effect has been imitated to a certain extent in optical devices such as stereoscopes and stereomicroscopes, so that the observer gets some impression of depth. In stereoscopes two photographs of an object are taken from different angles, and viewing lenses are used to direct images of the photographs to the eyes separately, so that one eye views only one of the photographs and the other eye views the other photograph. In a stereomicroscope two microscope systems are employed, one for each eye, so that each eye sees a slightly different view of the same object. This produces a stereoscopic effect but has limited field of view and depth of focus. Also since the eyes must be precisely positioned a very steady head position is required, and precise interpupillary distance adjustments must be made. Because microscopes involve a refractive lens system, the edges of wires and other sharp objects viewed tend to break down into "color fringes", producing fuzzy edges lacking good resolution. At high magnifications the stereoscopic effect is hard to control and may produce images which are flat and lack depth. Also, since the eyes must be stationary and precisely positioned, the object must be moved in order to see around edges.
Thus optical devices for producing a stereoscopic effect have conventionally involved using both eyes to superimpose two different images of the object. However, in U.S. Pat. No. 4,232,968, issued to the applicant in the present application, an optical comparator is described which produces a 3-D effect when the image is viewed by a single eye. In the optical comparator described in U.S. Pat. No. 4,232,968, images of two objects are projected in separate optical paths and are greatly enlarged. The resultant image shows the two objects side by side with a sharp dividing line. The exit pupil is substantially larger than the eye pupil of a viewer, and movement of the eye from side to side gives views of the object from different angles. This is apparently the source of the 3-D effect of this device.